Hydraulic blank holder



Dec. 15,1942, L; R. wlL AMsw 2.305.33

' HYDRAULIC BLANK HOLDER Filed April 20, 1939 2 Sheets-Sheet l INVENTORLLARK/N fF. WILLIAMSON RNY.

Dec. 15, 1942. 1.. R. WILLIAMSON HYDRAULIC BLANK HOLDER Filed A ril 20,1939 2 sheets-sham 2 R v ON M mm M E 0 R w W M W III M Fig.5

Patented Dec. 15, 1942 Uri-ire -HYDRAULIC BLANK HOLDER Larkin R.Williamson, Brooklyn, N. Y., assignor to E. W. Bliss Company, Brooklyn,N. Y., a corporation of Delaware Application April 20, 1939, Serial .No.268,961

5 Claims.

Inpresses of this type-heretofore used'it has I,

been customary to provide toggles to operate the blank holder .andgearing connecting the toggles and main drive of the press. Similarly,in triple action presses additional gearing, shafts and levers wererequired over that utilized to operatethe blank holder. These priorconstructions were expensive to build and were difiicult tosynchronizein such a manner that the load was uniformly applied in accord with apredetermined ratio. This has been particularly true in toggle-operatedblank holders where it was necessary to control the time and amount ofpressure applied ateach corner of the blank holder and the time it wasapplied.

The general object of my invention has been to provide a press in whichthe expensive and unwieldy gearing is eliminated and to employ hydraulicmeans to actuate the blank holder and related mechanism in either adouble or triple action press. An additional obiect has been to providemechanism associated with a blank holder to permit accurate control ofthe pressure applied at the corners thereof. Still another object hasbeen-to provide adjustments by which the relation between the forceapplied to the blank holder at any given point and the power means ofthe press may be varied as desired.

To the accomplishment of the foregoing and related ends, said invention,then, consists of the means hereinafter fully described and particularlypointed out in the claims; the annexed drawings and the followingdescriptionsetting forth in detail certain structure embodying theinvention, such disclosed means constituting, however, but one ofvarious structural forms in which the principle of the invention may beused.

In said annexed drawings- Fig. 1 is a perspective view of my improvedpress;

Fig. 2 is a view showing the hydraulic system employed;

Fig. 3 is a section through one of the pressure applying pistons and thesupply reservoir therefor;

Fig. 4 is a detail the system;

Fig. 5 shows a unit of the system by which an increased stroke isapplied to the blank holder showing an adjustment of over the strokeappliedto-the actuating piston; Fig. 6 is a similar view showing aconstruction by which an increased pressure at the blank holder isobtained over the pressure at the actuating piston; V

Fig. '7 is a detailof the safety mechanism; and Fig. 8 is a graphshowinghow the pressure applied to the blank holder may be controlled.

In general, my invention is preferably employed in connection with theblank holder -of a press. In such case four independent hydraulicsystems are employed which act at the four corners of the blank holderto push the same downwardly to grip a sheet. The systems are independentof each other to prevent one corner from acting as a-hydraulic fulcrumfor another. It will be apparent that more or fewer systems maybeemployedandthat the blank holder may receive the thrust of the hydraulicsystems at other thanthe'four corners. An air piston is provided to aidin -moving the blank holder against the work and to returnthe blankholder at the end of the drawing operation. Each separate systemcomprises an actuating piston driven from the press drive shaft, and asecond piston acting onthe blank holder which is moved upon actuation ofthe first'piston. A column of oil fills the space between the twopistons.

My invention contemplates varying the ratio between the actuating pistonand its related piston in each system, such that the ratio be tween thepressure applied and the pressure derived therefrom may be varied.Similarly, I contemplate varying the stroke of the blank holder withrespect to the stroke of the actuating piston. Additionally, the varioussystems which function as a unit to operate the blank holder may bevaried, one with respect to the other.

Referring now to the drawings, my press comprises the usual bed I!) anduprights II and I2 surmounted by a crown l5. A die slide 16 to sup-,

port the movable die is slidingly supported from the crown. The matingdie is carried in the customary manner on the bed.

The slide is reciprocated by a crankshaft l8 extending from right toleft and provided with two eccentric portions 20. The eccentrics carrypitmans 2!, which in turn engage the die slide to raise and lower thesame. A blank holder 23 is slidably carried in the uprights in ways 22secured thereto. The blank holder is of the usual configurationsurrounding the die slide.

Both the die slide and the blank holder are driven from the crankshaft[8 as hereafter described. The crankshaft in turn carries a pair of twingears 24 and 25 at opposite ends of the press. Each gear is providedwith a counterweight 2! to balance the crankshaft eccentrics. Thesegears are driven by pinions mounted in the usual manner on a back shaftextending across the press parallel to the crankshaft. The back shaft inturn is driven by a clutch shaft. A combined pulley wheel and flywheeltil is idly carried on the clutch shaft and is driven by a suitablesource of power. A clutch and brake mechanism is provided to drive theclutch shaft from the flywheel or to act as a brake to hold the clutchshaft with respect to the press frame.

To operate the blank holder, four independent hydraulic systems areprovided which coact as a unit with an air counterbalance cylinder 32and piston rod 33 to shift the blank holder downwardly into engagementwith the work. After the work stroke is finished the air counterbalance,carried by the crown in the usual manner, functions through the pistonrod secured to the blank holder to draw the same upwardly to theinactive position of Fig. 1.

The air cylinder provides a chamber on each side of the pistons (notshown) which is carried by a piston rod 33. As the operating cycle ofthe press begins air is admitted to the upper chamber above the pistonwith sufiicient pressure to push the blank holder down until it isalmost in contact with the work. At this time cam mechanism, hereafterdescribed, applies the hydraulic blank holding force to the blankholder. When the drawing operation is completed the air at the bottom ofthe cylinder, which is of the usual type, brings the blank holder up toits original position as soon as the air pressure above the piston andthe hydraulic pressure applied to the blank holder are removed.

Each individual hydraulic system comprises a pair of cylinders withpistons therein and a solid column of oil between the pistons totransmit the force applied at one to the other piston. Four systems areprovided and the pistons to which the actuating force is applied arepreferably mounted side by side, as shown in Fig. 2. These actuatingcylinders, indicated at 35 (Fig. 3) each comprise a, casing 36 capped atthe lower end at 3? and at the upper end at 38. The lower capthreadingly receives a pipe ii) passing to the blank holder.

A piston is slidingly received in the cylinder and protrudes through acap 38 to be engaged and moved by a, cam ii carried by the crankshaft.Each piston is of usual construction and comprises a disc :33 slidinglyreceived in a respective cylinder and held in sealing relation therewithby packing 44. A rod 5% extends upwardly from the disc 63, preferablynot integral therewith and is guided by a cap 38. The rod is provided atits end with a ball follower 5! which is in turn engaged by a cam llcarried on the crankshaft [8.

When the crankshaft rotates each of the cams 4i turn with it and onceduring each revolution will move the respective pistons 43 downwardlythrough the cylinder 35 to transmit an operating force to a piston 52 ina cylinder 54 carried above the blank holder at one of the four cornersthereof. The piston 52 carries a rod 55 which passes down to the blankholder and is bolted to a boss 55 thereof by nuts 57. Its stroke isequal to the stroke of the blank holder when the working dies are inplace and thus the length of the cylinders 54 should exceed this amount.The rod is guided in a slideway 58 integral with the machine crown.

It will be apparent that as the piston 43 is actuated it will transmitthe force applied to it through a solid column of fluid to itsassociated piston 52, which in turn will push the blank holder down inthe ways 22. The other three individual systems shown are identical toand in timed relation with the system described as an example. Theresult is to apply a, downward force at the four corners of the blankholder to move the same into gripping relation with the work.

To avoid loss of power each system is kept completely full of'oil, whichis supplied through a reservoir 60 connected by piping 6| into eachcylinder. In the piping Bl connecting each cylinder is a solenoidcontrolled valve which governs the passage of oil from the reservoir tothe cylinder.

Each cylinder is controlled individually by its separate valve to avoidany possibility of an uneven building up of pressure in the system andto avoid any fulcrum action between different parts of diiferentsystems. To this end, each valve and solenoid unit is electricallyconnected to and controlled by a limit switch 62, which in turn isopened and closed by a cam 64 on the crankshaft l8.

Only one valve is shown in Fig. 2, but it will be understood that aseparate valve unit is provided for each fluid system. As the shaft is1'0- tated the cam acts to operate the switch to close the valves to thereservoir just prior to the time when the respective cam 4i begins topush the respective piston 43 downwardly. After the blank holding strokeis finished the cam 64 allows the limit switch 53 to open, whichreleases the solenoid and opens the valves and allows oil to flow freelybetween the reservoir and the respective fluid systems.

To provide a safety mechanism in each fluid system and to control thepressure attained the spring controlled pistons, as shown in Fig. '7,are provided in each system. Each mechanism comprises a cylinder 65 inwhich is slidingly received a piston til, one side of which communicatesthrough piping 68 with the main pipe leading between two cylinders ofthe respective systern. Interposed between the piston and a disc iii inthe cylinder is a heavy calibrated spring 12 for urging fluid out of thecylinder. The resistanoe offered by the spring to movement of the pistonmay be varied by adjusting the position of the disc through the mediumof abolt (4 threadingly carried in the end of the cylinder wall. If itis desired to render a blank holder piston inactive at any predeterminedtime, or to decrease the pressure applied, the corresponding spring '12may be adjusted by the bolt 13 to collapse when this pressure isattained, thus limiting the pressure of that system by the strength ofthe spring 12. It will be apparent that by means of these pressurecylinders each system may be adjusted independently of the others or toprovide a given pressure ratio between the others.

To improve the drawing of the metal I have found that it is desirable toslightly decrease the blank holding pressure after the slide hascommenced the drawing operation. This insures that the proper amount ofmetal will flow from the region of the blank holder to form the finishedproduct between the dies. Fig. 8 illustrates how the pressure is builtup to a maximum point P and then is allowed to decrease slightly as at Lduring the part of the drawing operation where material is pulled fromthe part held by the blank holder. Thereafter, during the finishing partof the stroke the blank holding pressure is again built up to themaximum M, after which it is almost instantly released, when the pieceis removed from the press.

The pressure applied to the blank holder is controlled by shaping thecams M (Fig. 4) to provide two points 75 where the maximum down strokeis given the pistons 63 and a region H in between where the piston isallowed to rise slightly, thus relieving the blank holder pressure. Itwill be apparent that the cam configurations may be slightly varied onewith the other to obtain various desired pressure characteristics.

It is desirable to provide means to adjust the effective stroke of thepistons in the upper cylinders and in the blank holder cylinders E Tothis end the cylinders 35 are secured to the crown of the machine insuch manner as to be adjustable along the line of the piston axis, whichadjustment is effected by bolts 8i). After the particular cylinder 35 isclamped in an adjusted position bythe bolts suitable keys are insertedto prevent any movement of the cylinder during operation of, themachine. The position of the effective stroke of the blank holder may bevaried by adjusting the rods 55 in the bosses 55 and locking the rods bythe nuts 51.

The pressure applied by a system may be increased or decreased withrespect to the pressure applied to the piston 43 through the cams 41 byvarying the relative areas of the pistons 43 and 52. Thus, in any givenpress, blank holder mechanism may be employed which will provide alonger stroke of the blank holder than is indicated by the effectivethrow of the cams 4|. Conversely, a greater force but shorter stroke maybe applied to the blank holder than is applied by the earns 41 if theareas of the pistons 52 is made greater than the area of the pistons 43.

It is some times desirable to apply a greater force at one point of theblank holder than is applied at another. If this is to be apermanentfeature of the machine, it may be accomplished by varying the size ofthe pistons effective at that point on the blank holder over the size ofthe pistons effective elsewhere thereon. The same result may be attainedby varying the effective stroke of the pistons of one system as againstthe other systems.

Normally, any adjustment of pressure in the respective systems ispreferably attained by adjusting the calibrated springs to vary thepoint at which pressure rise due to cams 6i ceases by reason ofcollapsing of the springs.

If the press is to be employed as a triple action machine, an additionalcam or cams are provided to transmit the requisite force through theadditional fluid system or systems to perform the additional drawingoperation.

From the foregoing description it will be seen that I have provided anovel press which contains many less moving parts than has heretoforebeen necessary and which possesses marked advantages of simplicity,synchronism and ease of adjustment of movement over the pressesheretofore built.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being made as regards the structureherein disclosed, provided the means stated by any of the followingclaims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a press, a frame, a blank-holder slidably carried thereby, aplurality of hydraulically expansible means for actuating saidblank-holder, an individual source of hydraulic pressure for each ofsaid means, a common hydraulic fluid reservoir for supplying hydraulicfluid to all of said sources, and valves for individually sealing eachof said sources in either direction from each other and from saidreservoir.

2. In a press,,a frame, a blank holder slidably carried thereby, aplurality of hydraulically expansible means for actuating said blankholder, individual sources of hydraulic pressure one for each of saidmeans, a common hydraulic fluid reservoir for all of said sources, andvalves for simultaneously and individually completely sealing each ofsaid sources from each other and from said reservoir.

3. In a press, a frame, a reciprocable die slide carried thereby, ablank holder slidably carried thereby, a plurality of hydraulicallyexpansible means for actuating said blank holder, individual sources ofhydraulic pressure one for each of said means, a common hydraulic fluidreservoir for all of said sources, and valves responsive to thecommencement of the reciprocating cycle of said die slide forsimultaneously and individually sealing each of said sources from eachother and from said reservoir.

4. In a press, a frame, a blank-holder slidably carried thereby,hydraulic means for actuating said blank-holder, a rotatable cam and acam follower supported by said frame for actuating said hydraulic means,the cam having two spaced high points for varying the actuating forces,said first high point being adapted to cause a maximum piston stroke atthe start of the drawing operation and said second high point beingadapted to cause a maximum stroke during the finishing part of thedrawing operation, with a depressed portion between said high pointsadapted to cause release during that part of the drawing operation wherematerial is pulled from the part held by the blank holder, and means foradjustably spacing said cam from said cam follower whereby the effectivestroke of the actuating means of the blank-holder is varied.

5. In a press, a frame, a die slide therein, a blank holder slidablycarried by said frame, mechanical means to actuate said die slide,piston and cylinder means adapted upon admission of fluid to actuatesaid blank holder intoposition adjacent to the work and to return itautomatically afterwards, hydraulic means to actuate said blank holderinto a work engaging position, one end of saidcylinder means being deadwhereby actuation of said blank holder by fluid means compresses fluidbetween said end of said cylinder and said piston and when released bysaid hydraulic means returns the blank holder to its initial position.

LARKIN R. WILLIAMSON.

